The little girl's lung collapsed and she went into cardiac arrest Monday afternoon, her father, Michael Canahauati wrote in an update on her blog, Avery's Bucket List. Babies with severe types of SMA have difficulty regulating their breath and are especially vulnerable to respiratory complications.

"Avery's passing this quickly came as a complete shock to all of us, as she had just been given a thumbs up at her last doctor's appointment only three days ago," Mike Canahauati wrote in a blog post today. "While we were aware of the severity of her diagnosis, we never lost hope for Avery."

Her father wrote that the disease never took away Avery's smile and he shared a photo of Avery smiling before she was rushed to the hospital Monday.

On April 6, Avery was diagnosed with Type 1 SMA, or the most severe type of spinal muscular atrophy, an incurable, genetic disorder that attacks spinal neurons and progressively debilitates muscle function. Having Type 1, doctors gave Avery 18 months to live.

To cherish every moment with their daughter, the Canahuatis, from Bellaire, Tex., created "Avery's Bucket List," a sweet and joyful blog written from Avery's perspective, where they chronicle her world and track their family adventures, checking things off from the bucket list as they go.

Recently, Avery threw out the first pitch at a minor league baseball game in Houston, got a tattoo, a driver's license and had her first kiss.

Written in Avery's voice and infused with humor, the blog attracted millions of views online - from as far away as Malaysia, Hong Kong and Germany - as her story and message was shared through the SMA community, on Facebook and other social networking sites.

In her final post, written by her father, Avery writes: "When I started writing my blog, I thought I'd only be speaking to my closest friends and family members. Little did I know soooooooo many people would care about me and while I'm flattered to have so many people who love me, I hope they will also take time to love and care about all of my friends out there with SMA."

SMA is the No. 1 genetic killer of children under the age of 2 in the U.S., but many people don't know about it, Laura Canahuati explained in an interview before Avery's death. An estimated one in 40 people are carriers of SMA. If both parents are carriers, there's a 25 percent chance of their child having SMA.

The Canahuatis urge all parents to talk to their obstetricians and get tested to see if they carry the gene for SMA.

One of Avery's newest bucket list goals before her death was to raise $1 million towards SMA research and her parents wrote today that they want to help raise the remaining $365,000 for Avery's "SMA friends."

"Before Avery passed away, I made her a promise that I would continue to be an activist in raising SMA awareness, making genetic testing universally available, and in finding a cure for her friends," Mike Canahauti wrote. "I will not break that promise and in the name of SMA awareness and funding a cure, I hope parents of children everywhere will look at Avery's Bucket List and help her complete items she was unable to."

Research for treatment and a cure for SMA has come a long way over the last 10 years. Early clinical trials are underway, including the first ever trial for a drug designed specifically for SMA, according to Kenneth Hobby, president of the Families of SMA, an organization which funds research initiatives. Additional funds are devoted to promising gene therapies and ways to manage the symptoms. Currently, those with SMA Type I rarely live longer than 2 to 3 years.

While Avery did not cross off many items on her bucket list, her family hopes their daughter's story will raise awareness for the disease and help find a cure.